Plus it makes no sense. If they really hated it that much, they could simply quit (the Chineese government may be commies but they do not like slavery), so why commit suicide?
Yet another common misconception. The Chinese government has not been anything more than nominally communist since the days of Mao. The current Chinese government can be described as a single-party pro-business authoritarian regime with occasional streaks of socialism for the sole purpose of maintaining control. Cornerstones of communist regimes, such as widespread income redistribution and a state-controlled economy, are entirely absent in modern China.
Rural people who come to the big city to work in harsh conditions away from their families probably meet those two criteria especially well. They're overworked and lonely, and even though they're probably better fed, better paid, and maybe even better rested then they were home on the farm, psychologically they're under more pressure, and there really isn't anyone to keep an eye on them. So they have a day where the harsh conditions or pressures seem too much, and they jump off the building. And once the first person did it, people with a predisposition to suicide have that option hanging there in the back of their mind, and eventually do the same thing.